Acoustic data can be used in computers and consumer electronics for a variety of purposes. An ultrasonic (US) pen is one example. Some US pens can be used like a regular pen to write on a surface, such as a piece of paper or a whiteboard. At the same time however, the motion of the pen can be tracked using a combination of acoustics and electronics to capture the pen's motion.
US pen technology has many applications. For example, as a user writes on a surface, an image of the writing can be captured and shown on a computer display. This can be particularly useful for remote learning. For instance, as a teacher writes on a whiteboard during a class, the writing can be displayed on computer screens for students in the room as well as those located remotely.
As another example, rather than capturing an image of what is written on a surface, a US pen can also be used to move a mouse pointer in a graphical user interface. This can be particularly useful during presentations. For instance, presentations are commonly assembled on a computer and then projected onto a wall screen. With a US pen, a person can interact with the presentation directly from the image projected onto the screen. That is, the person can move the pen over the screen's surface, and the system can capture the motion of the pen and move an image of a mouse pointer on the screen to track the pen's motion. These are just two examples of the many ways in which US pen technology can be used.
Most US pen systems include at least two basic components, the US pen itself and a number of acoustic sensors. The pen usually gives off an inaudible, ultrasonic signal near an end of the pen. For example, the pen may generate the ultrasonic signal whenever the writing end of the pen is in contact with a surface. The acoustic sensors are usually microphones that are capable of detecting the ultrasonic signal. These sensors can be arrayed along one or more edges of a surface, or otherwise placed near the surface, so that two or more of the sensors can separately pick-up the ultrasonic signal from anywhere on the surface. Then, by comparing the signals from two or more of the acoustic sensors, the system can determine, or approximate, the position and motion of the pen on the surface. For example, based on the time delay between the ultrasonic signal as captured by two sensors, the speed of sound, and the relative locations of the two sensors, various algorithms can be used to triangulate a position of the pen and track the pen's motion as the position changes over time.